1. Field of the Invention
The present invention relates to an air bag that restrains mesh spreading and inflation gas leakage. The air bag may be used in a head-protecting air bag apparatus or a side-impact collision air bag apparatus mountable on a roof side rail part or the seat of an automobile.
2. Description of the Related Art
An air bag for a head-protecting air bag apparatus accommodated in a folded state in the edge portions of the openings of doors or windows in the interior of the vehicle is known in the art. During an inflow of an inflating gas, the air bag expands and inflates to cover the openings. This air bag has an inflation section with a wall portion made of a vehicle-interior-side wall and a vehicle-exterior-side wall. Inflation of the inflation section separates the vehicle-interior-side wall and the vehicle-exterior-side wall from each other by an air cushion.
In addition, plural linear joined portions are disposed in the area of the inflating section. The linear joined portions are formed to linearly join the opposed portions of the wall portion that constitutes the inflation section as shown in Japanese Patent Laid-Open No. 321535/1999. Such linear joined portions are disposed so that the peripheral and central portions of the inflating section have approximately the same thickness. The linear joined portions are disposed so that forward and rearward tensions are produced in the air bag when inflated. When forward and rearward stresses are produced in the air bag, the air bag does not move into the exterior of the vehicle even if the air bag receives a pressure which acts toward the exterior of the vehicle.
If the area of each of the end portions of the linear joined portions is small, stress concentration easily occurs in each of the end portions during the inflation of the inflating section. As a result, the wall portion which constitutes the inflating section is damaged in the vicinity of any of the end portions. To cope with this problem, wider end portions are used in the linear joined portions as shown, for example, in British Patent Laid-Open No. GB 2324068.
However, even when wider end portions are used, there are some cases where inflating gas leakage still occurs. Specifically, if the wall portion that constitutes the inflating section is strongly pulled during the inflation of the inflating section, mesh spreading occurs in the wall portion. Then, the inflating gas leaks from the spread meshes.
An aspect of this invention is to provide an air bag that can restrain the leakage of inflating gas from the vicinity of any of the end portions of the linear joined portions by reducing mesh spreading.
The air bag according to the invention is provided with an inflating section and linear joined portions. The inflation section, when receiving an inflow of an inflating gas, is inflated with opposing portions of its wall portion being spaced apart from each other. The linear joined portions are disposed in the inflation section and are formed to linearly join the opposing portions of the wall portion in the inflation section. Each of the linear joined portions includes a body portion and end portions. The end portions are disposed at each end of the body portion. The end portions gradually become wider than the body portion. A periphery surrounds each of the end portions and the periphery is provided with at least three straight portions that surround the end portions.
During inflation of the air bag, each of the end portions of the linear joined portions is surrounded by swollen portions that isolate opposed walls from each other near each of the end portions. Accordingly, the swollen portions are respectively disposed adjacent to the straight portions of the periphery of each of the end portions in such a manner as to be brought into linear contact with each of the end portions along wide straight lines. The swollen portions are not disposed to come into partial contact with the straight portions. Accordingly, in the air bag according to the invention, stress concentration does not easily occur in the boundary portion between any of the end portions and the swollen portions, and spreading of the meshes of yarns that weave the air bag is prevented. This, in turn prevents inflating gas from leaking from the boundary portion between any of the end portions and the swollen portions.
In addition, if the number of the straight portions that constitute each periphery of the end portions is at least three, approximately the entire area of each periphery of the respective end portions can be formed of straight portions, except the body portions. Accordingly, it is possible to restrain the leakage of inflating gas from the vicinity of any of the end portions of the linear joined portions.
Since each of the straight portions is disposed in parallel with yarns that weave the air bag, it is possible to obtain the following effects and advantages. Specifically, even if the wall portion is strongly pulled at the swollen portions located adjacent to the respective straight portions, the forces exerted by the pulling are approximately parallel or perpendicular to the yarns. Since the pulling directions during inflation differ from the bias directions of the yarns, it is possible to prevent mesh spreading to a further extent.